/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.log4j;

import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.helpers.PatternParser;
import org.apache.log4j.helpers.PatternConverter;

// Contributors:   Nelson Minar <nelson@monkey.org>
//                 Anders Kristensen <akristensen@dynamicsoft.com>

/**
 * A flexible layout configurable with pattern string.
 * 
 * This code is known to have synchronization and other issues which are not
 * present in org.apache.log4j.EnhancedPatternLayout. EnhancedPatternLayout
 * should be used in preference to PatternLayout. EnhancedPatternLayout is
 * distributed in the log4j extras companion.
 * 
 * <p>
 * The goal of this class is to {@link #format format} a {@link LoggingEvent}
 * and return the results as a String. The results depend on the
 * <em>conversion pattern</em>.
 * 
 * <p>
 * The conversion pattern is closely related to the conversion pattern of the
 * printf function in C. A conversion pattern is composed of literal text and
 * format control expressions called <em>conversion specifiers</em>.
 * 
 * <p>
 * <i>You are free to insert any literal text within the conversion pattern.</i>
 * 
 * <p>
 * Each conversion specifier starts with a percent sign (%) and is followed by
 * optional <em>format modifiers</em> and a <em>conversion
   character</em>. The conversion
 * character specifies the type of data, e.g. category, priority, date, thread
 * name. The format modifiers control such things as field width, padding, left
 * and right justification. The following is a simple example.
 * 
 * <p>
 * Let the conversion pattern be <b>"%-5p [%t]: %m%n"</b> and assume that the
 * log4j environment was set to use a PatternLayout. Then the statements
 * 
 * <pre>
 * Category root = Category.getRoot();
 * root.debug(&quot;Message 1&quot;);
 * root.warn(&quot;Message 2&quot;);
 * </pre>
 * 
 * would yield the output
 * 
 * <pre>
 *    DEBUG [main]: Message 1
 *    WARN  [main]: Message 2
 * </pre>
 * 
 * <p>
 * Note that there is no explicit separator between text and conversion
 * specifiers. The pattern parser knows when it has reached the end of a
 * conversion specifier when it reads a conversion character. In the example
 * above the conversion specifier <b>%-5p</b> means the priority of the logging
 * event should be left justified to a width of five characters.
 * 
 * The recognized conversion characters are
 * 
 * <p>
 * <table border="1" CELLPADDING="8">
 * <th>Conversion Character</th>
 * <th>Effect</th>
 * 
 * <tr>
 * <td align=center><b>c</b></td>
 * 
 * <td>Used to output the category of the logging event. The category conversion
 * specifier can be optionally followed by <em>precision specifier</em>, that is
 * a decimal constant in brackets.
 * 
 * <p>
 * If a precision specifier is given, then only the corresponding number of
 * right most components of the category name will be printed. By default the
 * category name is printed in full.
 * 
 * <p>
 * For example, for the category name "a.b.c" the pattern <b>%c{2}</b> will
 * output "b.c".
 * 
 * </td>
 * </tr>
 * 
 * <tr>
 * <td align=center><b>C</b></td>
 * 
 * <td>Used to output the fully qualified class name of the caller issuing the
 * logging request. This conversion specifier can be optionally followed by
 * <em>precision specifier</em>, that is a decimal constant in brackets.
 * 
 * <p>
 * If a precision specifier is given, then only the corresponding number of
 * right most components of the class name will be printed. By default the class
 * name is output in fully qualified form.
 * 
 * <p>
 * For example, for the class name "org.apache.xyz.SomeClass", the pattern
 * <b>%C{1}</b> will output "SomeClass".
 * 
 * <p>
 * <b>WARNING</b> Generating the caller class information is slow. Thus, use
 * should be avoided unless execution speed is not an issue.
 * 
 * </td>
 * </tr>
 * 
 * <tr>
 * <td align=center><b>d</b></td>
 * <td>Used to output the date of the logging event. The date conversion
 * specifier may be followed by a <em>date format specifier</em> enclosed
 * between braces. For example, <b>%d{HH:mm:ss,SSS}</b> or
 * <b>%d{dd&nbsp;MMM&nbsp;yyyy&nbsp;HH:mm:ss,SSS}</b>. If no date format
 * specifier is given then ISO8601 format is assumed.
 * 
 * <p>
 * The date format specifier admits the same syntax as the time pattern string
 * of the {@link java.text.SimpleDateFormat}. Although part of the standard JDK,
 * the performance of <code>SimpleDateFormat</code> is quite poor.
 * 
 * <p>
 * For better results it is recommended to use the log4j date formatters. These
 * can be specified using one of the strings "ABSOLUTE", "DATE" and "ISO8601"
 * for specifying {@link org.apache.log4j.helpers.AbsoluteTimeDateFormat
 * AbsoluteTimeDateFormat}, {@link org.apache.log4j.helpers.DateTimeDateFormat
 * DateTimeDateFormat} and respectively
 * {@link org.apache.log4j.helpers.ISO8601DateFormat ISO8601DateFormat}. For
 * example, <b>%d{ISO8601}</b> or <b>%d{ABSOLUTE}</b>.
 * 
 * <p>
 * These dedicated date formatters perform significantly better than
 * {@link java.text.SimpleDateFormat}.</td>
 * </tr>
 * 
 * <tr>
 * <td align=center><b>F</b></td>
 * 
 * <td>Used to output the file name where the logging request was issued.
 * 
 * <p>
 * <b>WARNING</b> Generating caller location information is extremely slow and
 * should be avoided unless execution speed is not an issue.
 * 
 * </tr>
 * 
 * <tr>
 * <td align=center><b>l</b></td>
 * 
 * <td>Used to output location information of the caller which generated the
 * logging event.
 * 
 * <p>
 * The location information depends on the JVM implementation but usually
 * consists of the fully qualified name of the calling method followed by the
 * callers source the file name and line number between parentheses.
 * 
 * <p>
 * The location information can be very useful. However, its generation is
 * <em>extremely</em> slow and should be avoided unless execution speed is not
 * an issue.
 * 
 * </td>
 * </tr>
 * 
 * <tr>
 * <td align=center><b>L</b></td>
 * 
 * <td>Used to output the line number from where the logging request was issued.
 * 
 * <p>
 * <b>WARNING</b> Generating caller location information is extremely slow and
 * should be avoided unless execution speed is not an issue.
 * 
 * </tr>
 * 
 * 
 * <tr>
 * <td align=center><b>m</b></td>
 * <td>Used to output the application supplied message associated with the
 * logging event.</td>
 * </tr>
 * 
 * <tr>
 * <td align=center><b>M</b></td>
 * 
 * <td>Used to output the method name where the logging request was issued.
 * 
 * <p>
 * <b>WARNING</b> Generating caller location information is extremely slow and
 * should be avoided unless execution speed is not an issue.
 * 
 * </tr>
 * 
 * <tr>
 * <td align=center><b>n</b></td>
 * 
 * <td>Outputs the platform dependent line separator character or characters.
 * 
 * <p>
 * This conversion character offers practically the same performance as using
 * non-portable line separator strings such as "\n", or "\r\n". Thus, it is the
 * preferred way of specifying a line separator.
 * 
 * 
 * </tr>
 * 
 * <tr>
 * <td align=center><b>p</b></td>
 * <td>Used to output the priority of the logging event.</td>
 * </tr>
 * 
 * <tr>
 * 
 * <td align=center><b>r</b></td>
 * 
 * <td>Used to output the number of milliseconds elapsed from the construction
 * of the layout until the creation of the logging event.</td>
 * </tr>
 * 
 * 
 * <tr>
 * <td align=center><b>t</b></td>
 * 
 * <td>Used to output the name of the thread that generated the logging event.</td>
 * 
 * </tr>
 * 
 * <tr>
 * 
 * <td align=center><b>x</b></td>
 * 
 * <td>Used to output the NDC (nested diagnostic context) associated with the
 * thread that generated the logging event.</td>
 * </tr>
 * 
 * 
 * <tr>
 * <td align=center><b>X</b></td>
 * 
 * <td>
 * 
 * <p>
 * Used to output the MDC (mapped diagnostic context) associated with the thread
 * that generated the logging event. The <b>X</b> conversion character
 * <em>must</em> be followed by the key for the map placed between braces, as in
 * <b>%X{clientNumber}</b> where <code>clientNumber</code> is the key. The value
 * in the MDC corresponding to the key will be output.
 * </p>
 * 
 * <p>
 * See {@link MDC} class for more details.
 * </p>
 * 
 * </td>
 * </tr>
 * 
 * <tr>
 * 
 * <td align=center><b>%</b></td>
 * 
 * <td>The sequence %% outputs a single percent sign.</td>
 * </tr>
 * 
 * </table>
 * 
 * <p>
 * By default the relevant information is output as is. However, with the aid of
 * format modifiers it is possible to change the minimum field width, the
 * maximum field width and justification.
 * 
 * <p>
 * The optional format modifier is placed between the percent sign and the
 * conversion character.
 * 
 * <p>
 * The first optional format modifier is the <em>left justification
   flag</em> which is just the minus
 * (-) character. Then comes the optional <em>minimum field width</em> modifier.
 * This is a decimal constant that represents the minimum number of characters
 * to output. If the data item requires fewer characters, it is padded on either
 * the left or the right until the minimum width is reached. The default is to
 * pad on the left (right justify) but you can specify right padding with the
 * left justification flag. The padding character is space. If the data item is
 * larger than the minimum field width, the field is expanded to accommodate the
 * data. The value is never truncated.
 * 
 * <p>
 * This behavior can be changed using the <em>maximum field
   width</em> modifier which is
 * designated by a period followed by a decimal constant. If the data item is
 * longer than the maximum field, then the extra characters are removed from the
 * <em>beginning</em> of the data item and not from the end. For example, it the
 * maximum field width is eight and the data item is ten characters long, then
 * the first two characters of the data item are dropped. This behavior deviates
 * from the printf function in C where truncation is done from the end.
 * 
 * <p>
 * Below are various format modifier examples for the category conversion
 * specifier.
 * 
 * <p>
 * <TABLE BORDER=1 CELLPADDING=8>
 * <th>Format modifier
 * <th>left justify
 * <th>minimum width
 * <th>maximum width
 * <th>comment
 * 
 * <tr>
 * <td align=center>%20c</td>
 * <td align=center>false</td>
 * <td align=center>20</td>
 * <td align=center>none</td>
 * 
 * <td>Left pad with spaces if the category name is less than 20 characters
 * long.
 * 
 * <tr>
 * <td align=center>%-20c</td>
 * <td align=center>true</td>
 * <td align=center>20</td>
 * <td align=center>none</td>
 * <td>Right pad with spaces if the category name is less than 20 characters
 * long.
 * 
 * <tr>
 * <td align=center>%.30c</td>
 * <td align=center>NA</td>
 * <td align=center>none</td>
 * <td align=center>30</td>
 * 
 * <td>Truncate from the beginning if the category name is longer than 30
 * characters.
 * 
 * <tr>
 * <td align=center>%20.30c</td>
 * <td align=center>false</td>
 * <td align=center>20</td>
 * <td align=center>30</td>
 * 
 * <td>Left pad with spaces if the category name is shorter than 20 characters.
 * However, if category name is longer than 30 characters, then truncate from
 * the beginning.
 * 
 * <tr>
 * <td align=center>%-20.30c</td>
 * <td align=center>true</td>
 * <td align=center>20</td>
 * <td align=center>30</td>
 * 
 * <td>Right pad with spaces if the category name is shorter than 20 characters.
 * However, if category name is longer than 30 characters, then truncate from
 * the beginning.
 * 
 * </table>
 * 
 * <p>
 * Below are some examples of conversion patterns.
 * 
 * <dl>
 * 
 * <p>
 * <dt><b>%r [%t] %-5p %c %x - %m%n</b>
 * <p>
 * <dd>This is essentially the TTCC layout.
 * 
 * <p>
 * <dt><b>%-6r [%15.15t] %-5p %30.30c %x - %m%n</b>
 * 
 * <p>
 * <dd>Similar to the TTCC layout except that the relative time is right padded
 * if less than 6 digits, thread name is right padded if less than 15 characters
 * and truncated if longer and the category name is left padded if shorter than
 * 30 characters and truncated if longer.
 * 
 * </dl>
 * 
 * <p>
 * The above text is largely inspired from Peter A. Darnell and Philip E.
 * Margolis' highly recommended book "C -- a Software Engineering Approach",
 * ISBN 0-387-97389-3.
 * 
 * @author <a href="mailto:cakalijp@Maritz.com">James P. Cakalic</a>
 * @author Ceki G&uuml;lc&uuml;
 * @since 0.8.2
 */
public class PatternLayout extends Layout {

	/**
	 * Default pattern string for log output. Currently set to the string
	 * <b>"%m%n"</b> which just prints the application supplied message.
	 */
	public final static String DEFAULT_CONVERSION_PATTERN = "%m%n";

	/**
	 * A conversion pattern equivalent to the TTCCCLayout. Current value is
	 * <b>%r [%t] %p %c %x - %m%n</b>.
	 */
	public final static String TTCC_CONVERSION_PATTERN = "%r [%t] %p %c %x - %m%n";

	protected final int BUF_SIZE = 256;
	protected final int MAX_CAPACITY = 1024;

	// output buffer appended to when format() is invoked
	private StringBuffer sbuf = new StringBuffer(BUF_SIZE);

	private String pattern;

	private PatternConverter head;

	/**
	 * Constructs a PatternLayout using the DEFAULT_LAYOUT_PATTERN.
	 * 
	 * The default pattern just produces the application supplied message.
	 */
	public PatternLayout() {
		this(DEFAULT_CONVERSION_PATTERN);
	}

	/**
	 * Constructs a PatternLayout using the supplied conversion pattern.
	 */
	public PatternLayout(String pattern) {
		this.pattern = pattern;
		head = createPatternParser(
				(pattern == null) ? DEFAULT_CONVERSION_PATTERN : pattern)
				.parse();
	}

	/**
	 * Set the <b>ConversionPattern</b> option. This is the string which
	 * controls formatting and consists of a mix of literal content and
	 * conversion specifiers.
	 */
	public void setConversionPattern(String conversionPattern) {
		pattern = conversionPattern;
		head = createPatternParser(conversionPattern).parse();
	}

	/**
	 * Returns the value of the <b>ConversionPattern</b> option.
	 */
	public String getConversionPattern() {
		return pattern;
	}

	/**
	 * Does not do anything as options become effective
	 */
	public void activateOptions() {
		// nothing to do.
	}

	/**
	 * The PatternLayout does not handle the throwable contained within
	 * {@link LoggingEvent LoggingEvents}. Thus, it returns <code>true</code>.
	 * 
	 * @since 0.8.4
	 */
	public boolean ignoresThrowable() {
		return true;
	}

	/**
	 * Returns PatternParser used to parse the conversion string. Subclasses may
	 * override this to return a subclass of PatternParser which recognize
	 * custom conversion characters.
	 * 
	 * @since 0.9.0
	 */
	protected PatternParser createPatternParser(String pattern) {
		return new PatternParser(pattern);
	}

	/**
	 * Produces a formatted string as specified by the conversion pattern.
	 */
	public String format(LoggingEvent event) {
		// Reset working stringbuffer
		if (sbuf.capacity() > MAX_CAPACITY) {
			sbuf = new StringBuffer(BUF_SIZE);
		} else {
			sbuf.setLength(0);
		}

		PatternConverter c = head;

		while (c != null) {
			c.format(sbuf, event);
			c = c.next;
		}
		return sbuf.toString();
	}
}
